NASA has erased the city-killer asteroid’s chance of hitting the Moon in 2032

NASA’s Center for Near-Earth Object Studies has ruled out any chance that asteroid 2024 YR4 will strike the Moon in 2032, closing the door on a risk that had climbed to several percent over the past year. The determination, announced March 5, 2026, rests on new observations from the James Webb Space Telescope that extended astronomers’ view of the object’s orbit and pinned down its future position with far more precision than earlier data allowed. Nicknamed a “city-killer” for its size, the roughly 200-foot-wide asteroid is now projected to pass the Moon at a safe distance of about 13,200 miles on December 22, 2032.

From a Record Earth Risk to a New Moon Concern

Discovered in December 2024 by the ATLAS survey, 2024 YR4 initially climbed to one of the highest Earth-impact probabilities ever recorded for an asteroid of its size, briefly reaching Level 3 on the Torino Impact Hazard Scale, a rating reserved for close encounters that merit attention from astronomers and the public alike. Additional tracking through February 2025 steadily narrowed the uncertainty in its orbit, and by that month the chance of an Earth impact had dropped low enough that the object was reassigned to Torino Scale Level 0, meaning no significant hazard. Because the same refined orbit passed close to the Moon’s neighborhood, though, astronomers using Webb and ground-based telescopes calculated a newly nonzero lunar impact probability, an estimate that stood at 4.3 percent based on data gathered earlier in 2025 and was later refined to 3.8 percent by that April, keeping the object under close watch even after Earth itself was cleared.

A City-Sized Rock, Measured Precisely for the First Time

Part of what made the asteroid newsworthy in the first place was its size. Ground-based estimates originally put 2024 YR4 at roughly 130 to 300 feet across, a wide enough range that its potential effects were hard to characterize. Webb’s infrared instruments changed that in the spring of 2025, directly measuring the object’s thermal glow rather than relying only on reflected sunlight, and pinning its diameter at about 200 feet, roughly the height of a 15-story building. An object that size, were it ever to strike a populated area, could level a city block, which is where the informal “city-killer” nickname came from, even though NASA’s own updates have consistently stressed that the label refers to the asteroid’s physical scale rather than its likelihood of ever reaching Earth or the Moon.

Why an Asteroid This Size Was So Hard to Pin Down

Part of what made 2024 YR4 difficult to track precisely is simply how faint it is. According to the NASA Webb mission team, the asteroid currently reflects about as much light as an almond would at the distance of the Moon, glowing at roughly magnitude 30, some 4 billion times fainter than the faintest star visible to the naked eye. Webb was the only observatory sensitive and stable enough to track a moving target that dim while holding it steady across hour-long exposures, and no other telescope on Earth or in space will be able to observe 2024 YR4 again until it makes its next close pass through the inner solar system in 2028.

A Discretionary Observing Run Closes the Gap

To resolve the uncertainty before then, NASA granted Webb director’s discretionary time to a team led by Andy Rivkin of the Johns Hopkins University Applied Physics Laboratory and Julien de Wit of the Massachusetts Institute of Technology. Their observations, taken February 18 and 26, 2026, extended the period over which 2024 YR4 had been tracked from May 2025 to late February 2026, nearly doubling the length of the observational baseline. That longer baseline, combined with the precision of Webb’s measurements, gave orbital dynamicists far greater confidence in projecting exactly where the asteroid will be on December 22, 2032.

A Fraction of an Arcsecond Decided the Outcome

The result turned out to be unambiguous. Webb detected the asteroid at a position offset by about 22 pixels, roughly half an arcsecond, from where it would have needed to be to support any real chance of a lunar impact. That gap was enough for NASA to formally eliminate the possibility of 2024 YR4 striking the Moon in 2032, replacing the earlier probability estimates with a clean miss projected at 13,200 miles, a comfortable margin by planetary-defense standards. NASA’s own asteroid tracking page notes the object has fallen from the highest-profile impact scare in the Sentry risk table’s history to a case now considered fully resolved for Earth and the Moon alike.

A Preview of How Future Threats Will Be Assessed

Beyond settling the fate of one 200-foot asteroid, the episode doubled as a test of how NASA can use Webb’s unique capabilities for planetary defense years before an object becomes observable again by other means. Rivkin and de Wit noted that the techniques their team developed to isolate such a faint, fast-moving target against a field of much brighter stars can be reapplied the next time a newly discovered object needs urgent follow-up. NASA has also pointed to upcoming assets, including the Nancy Grace Roman Space Telescope and the dedicated Near-Earth Object Surveyor, as tools that could extend this kind of early orbit refinement to a wider range of potentially hazardous objects before they require this level of last-minute scrutiny.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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